Visual acuity charts are commonly used to measure visual acuity because they are standardized and easy to use, and can be widely distributed. Testing of visual acuity typically involves asking a patient to identify optotypes—visual patterns of letters or objects—presented on a test slide (or series of slides). Each slide includes one or more optotypes, arranged in one or more lines at one time. The patient's ability to identify optotypes as a function of their size is registered and scored to yield an estimate of visual acuity. The estimate of visual acuity obtained, e.g., the smallest optotype size that the patient can reliably see, can depend fundamentally on the design of testing and scoring, which is based on pre-determined rules and heuristics specific to each chart.